The present invention relates to an optical head, a method for manufacturing an optical head, and an optical disk apparatus.
Conventionally, the optical heads (namely, optical pick up) are known in the art, for instance, from JP-A-64-46242 and JP-A-64-43822.
The optical head described in JP-A-64-46242 is so constructed that the surface emitting laser and the photodetector are formed on the same substrate, the glass plates are stacked, or laminated on this substrate, and the focusing grating coupler (hologram lens) is fabricated on the surface of this glass plate.
On the other hand, the optical head described in JP-A-64-43822 is so arranged that the above-described optical head disclosed in JP-A-64-46242 is employed as the optical head main body, and this optical head main body is mounted on the flying slider.
In the optical head disclosed in JP-A-64-46242, the focusing grating coupler is utilized. In case of such a focusing grating coupler, chromatic aberration is large when the wavelength of the light from the light source is varied due to temperature variations and the like. Although this prior art describes that there is no change in the wavelengths when the surface emitting laser is employed, there is adverse influence since the wavelength is changed by the temperatures, as apparent from the publication xe2x80x9cSURFACE EMITTING LASERxe2x80x9d written by Iga, FIG. 12, page 8, vol. 60, No. 1, APPLIED PHYSICS, 1991. Accordingly, this prior art owns such a problem that no solution means is taken to the wavelength variation.
Furthermore, as to the optical head described in JP-A-64-46242, the optical path to the optical disk is inclined in order to separate the optical path for the laser light emitted from the surface emitting laser to the optical disk, from the optical path for the light returned from the optical disk to the photodetector. When the optical path is inclined, there is a problem that aberration and also asymmetrical strength distributions may easily occur, resulting in a large spot size of the laser light. It should be noted that the applications of the SCOOP structure have been proposed in this prior art, taking account of such a problem caused by the inclined optical path. However, since only differences in reflectivities of the medium can be detected in case of the SCOOP structure, there are drawbacks that neither the tracking signal, nor the opto-magnetic signal can be detected.
On the other hand, in the optical head described in JP-A-64-43822, since the optical head is mounted on the flying slider separately manufactured, it is very difficult to adjust the slider surface and the optical head within the normal focal depth from 2 micrometers to 3 micrometers. If the automatic focusing control would be performed, then this focal depth adjustment would not be required. However, since JP-A-64-43822 has such an object that this automatic focusing control is not performed, the above-explained difficult focal depth adjustment must be carried out.
It should also be noted that JP-A-64-43822 never discloses a method for manufacturing an optical head with employment of a surface emitting laser, and also an optical disk apparatus suitable for a flying type optical head.
A primary object of the present invention is therefore to provide an optical head capable of reducing chromatic aberration caused when wavelengths of light emitted from a light source are changed due to a variation in temperatures.
A secondary object of the present invention is to provide an improved optical head capable of preventing the above-explained problems caused by the SCOOP structure and by inclining an optical path with respect to an optical disk.
A third object of the present invention is to provide a flying type optical head which deprives such a positional adjustment between a flying slider and this optical head.
A fourth object of the present invention is to provide a method for manufacturing an optical head with employment of a surface emitting laser.
A fifth object of the present invention is to provide an optical disk apparatus suitable for a flying type optical head.
In accordance with a first aspect of the present invention, it is provided an optical head that a semiconductor laser is formed via a buffer layer on a substrate, and an opening portion is fabricated in the substrate at a lower portion of a laser emitting surface;
said opening portion is furthermore filled with a transparent layer;
one of a grating lens, a distributed index lens, and a condenser lens made of a convex lens having a diameter less than 1 mm is formed on a lower surface of said transparent layer.
According to a second aspect of the present invention, it is provided such an optical disk that a semiconductor laser and a photodetector are formed via a buffer layer on the same substrate in such a manner that a laser light emitting surface of the semiconductor laser and a light receiving surface of said photodetector are directed to the same direction, and an opening is fabricated under said laser emitting surface and said light receiving surface;
further, a first transparent layer for filling the opening portion is stacked;
a diffraction grating is formed on a lower surface of said first transparent layer;
a second transparent layer is stacked on a lower surface of said first transparent layer; and
a condenser lens constructed of a grating lens, a distributed index lens, or a convex lens is formed on a lower surface of said transparent layer;
wherein laser light emitted from said semiconductor laser is penetrated through said substrate, said first transparent layer, said diffraction grating, and said second transparent layer, and condensed toward a place just under the condenser lens, by said condenser lens, thereby forming a light spot on an optical storage medium positioned apart from said condenser lens, whereas reflection light reflected from said optical storage medium is penetrated through said condenser lens and said second transparent layer, diffracted by said diffraction grating toward a light receiving plane of said photodetector, and further penetrated through said first transparent layer to be received by said photodetector.
In accordance with a third aspect of the present invention, it is provided an optical head that a shape of said optical head (106) is processed to become a flying slider shape in an one body.
According to a fourth aspect of the present invention, it is provided a method for manufacturing an optical head wherein a semiconductor laser and a photodetector are formed via a buffer layer on the same substrate in such a manner that a laser light emitting surface of the semiconductor laser and a light receiving surface of said photodetector are directed to the same direction, and an opening is fabricated under said laser emitting surface and said light receiving surface by an etching process, characterized by comprising the steps of:
stacking a first transparent layer used to fill said opening by way of the plasma CVD (Chemical vapor deposition) and sputtering processes;
forming a second transparent layer under said first transparent layer by way of the plasma CVD, and sputtering processes; and
forming either a grating lens on a lower surface of said second transparent layer by way of the photomask exposure process, or one of a distributed index lens and a convex lens on said lower surface of said second transparent layer by way of the ion exchange process.
Furthermore, according to the present invention, it may be provided a method for manufacturing an optical head in which a surface emitting laser and a photodiode are manufactured at the same time in accordance with the following processing steps (a) to (f), characterized by comprising the steps wherein:
(a). an n type AlGaAs buffer layer is grown on an n type GaAs substrate, an n type GaAs layer is grown on said buffer layer, and a first reflection mirror layer constructed by alternately stacking n type AlAs layers and GaAlAs layers is formed on said n+ type GaAs layer;
(b). said first reflection mirror layer is removed by way of an etching process only from a portion where said photodiode is to be manufactured, and an n type AlGaAs layer, is grown on the layer removed portion;
(c). an n type AlGaAs clad layer is formed on said first reflection mirror layer and said n type AlGaAs layer, a p type GaAlAs quantum well layer is grown on said clad layer as an activate layer, a p type GaAlAs clad layer is fabricated on said activate layer; and a second reflection mirror layer constructed by alternately stacking n type AlAs layers and GaAlAs layers is grown on said clad layer;
(d). said second reflection mirror layer is removed by way of the etching process only from the portion where the photodiode is to be formed, and a p type GaAs layer is formed on the removed portion;
(e). a p+ type GaAs layer is formed on said second reflection mirror layer and said p type GaAs layer, on which an Au electrode is formed; and
(f). a groove for separating said surface emitting laser from said photodiode is formed.
In accordance with a fifth aspect of the present invention, it is provided an optical disk apparatus comprising:
a flying type optical head whose flying amount is smaller than, or equal to 26 micrometers;
an optical disk having no transparent protection layer on the information reading side of the recording surface thereof, or having a transparent protection layer with a thickness less than a value obtained by subtracting said flying amount from a back focus distance of an object lens located within a medium whose refractive index is 1.0, and by multiplying the subtraction result by a refractive index of a protection layer;
a supporting mechanism for supporting said optical head; and
a dust-guard cartridge for containing at least said optical disk, said optical head, and said supporting mechanism.
In the optical head according to the first aspect of the present invention, since the semiconductor laser is formed via the buffer layer and the opening portion is fabricated on the lower portion of the laser light emitting surface of the substrate, attenuation of the layer light is lowered. As previously discussed the condenser lens having the diameter smaller than, or equal to 1 mm is formed on the lower surface of the transparent layer stacked under the substrate. When the diameter of the condenser lens is selected to be smaller than, or equal to 1 mm, as will be explained later, the wave front precision of 0.1 xcex can be realized even when the variations in wavelengths become xcex94xcex=3 nm, so that there is no problem about chromatic aberration caused by the variation in the wavelengths of the light emitted from the light source due to the temperature changes.
In the optical head according to the second aspect of the present invention, the diffraction grating is provided between the semiconductor laser and the condenser lens, the laser light projected from the condenser lens and reflected by the optical storage medium, is again incident upon this condenser lens, and thereafter this reflected laser light is directed toward the light receiving surface of the photodetector capable of detecting the tracking signal and the opto-magnetic signal. As a result, this optical head can prevent the conventional problems caused by setting the optical path to be inclined with respect to the optical disk and by the SCOOP structure.
In the optical disk according to the third aspect of the present invention, and the flying slider is formed with the optical head main body in an integral form, and the film thickness of the ceramic material such as zirconia is controlled and is formed by way of the sputtering process, so that the positioning adjustment between the flying slider and the optical head is no longer required.
In accordance with the method for manufacturing the optical head of the fourth aspect of the present invention, the optical head of the present invention can be manufactured by employing the semiconductor process such as the photomask exposure process. Also, both the surface emitting laser and the photodiode can be manufactured at the same time.
In the optical disk apparatus according to the fifth aspect of the present invention, the flying type optical head whose flying amount is smaller than, or equal to 20 micrometers, and the below-mentioned optical disk are employed. That is, this optical disk has either no transparent protection layer at the information reading side of the storage surface thereof, or a transparent protection layer whose thickness is less than a value obtained by subtracting the flying amount from the back focus distance of the object lens located within the medium whose refractive index is 1.0, and by multiplying the subtraction result by a refractive index of the protection layer. As will be described later, when the flying amount is below than 26 micrometers, the flying variation amount is below than 2.6 micrometers, so that this flying variation amount can be absorbed by the focal depth of the condenser lens. As a result, the recording surface can be read without the defocusing control. When the thickness of the protection layer becomes thin, the optical disk may be damaged by dust. Therefore, since this optical disk is contained into the dust-guard cartridge, there is no practical problem in using the optical disk.